Carpet and carpet tiles having cushioned backings are well known to those of skill in the art. Such cushioned backed carpet is disclosed, for example in my U.S. Pat. No. 4,522,857 (incorporated by reference). An example of a prior art tufted carpet product is illustrated in FIG. 1A and an example of a prior art bonded carpet product is illustrated in FIG. 1B herein.
In the prior art tufted carpet, a primary carpet fabric 12 is embedded in an adhesive layer 16 in which is embedded a layer of glass scrim or nonwoven material. A foam base composite 19 is likewise adhesively bonded to the adhesive layer 16. In the prior art tufted carpet illustrated in FIG. 1A, the primary carpet fabric 12 includes a loop pile layer 20 tufted through a primary backing 22 by a conventional tufting process and held in place by a precoat backing layer of latex 24 or other appropriate adhesive including a hot melt adhesive or the like. The foam base composite 19 of the prior art tufted carpet product preferably includes an intermediate layer 26 molded to a layer of urethane foam 28 as illustrated.
The bonded carpet product (FIG. 1B) formed according to the prior art employs the same type of foam base composite 19 adhesively bonded by adhesive laminate layers 16. However, the primary carpet fabric 12 has somewhat different components from that of the tufted product in that it preferably comprises cut pile yarns 34 implanted in a PVC, latex, or hot melt adhesive 36 having a woven or nonwoven reinforcement or substrate layer 38 of fiberglass, nylon, polypropylene or polyester.
In the potentially preferred embodiment of the present invention, a puddle of polyurethane-forming composition is deposited across a nonwoven needlepunched backing material of polyester and polypropylene. A primary carpet fabric which may include a glass reinforcement material bonded thereto is brought together with the polyurethane-forming puddle. The entire structure is then heated to cure the polyurethane forming composition.
It has been determined that through proper control of the composition of the nonwoven backing that significant advantages in heat shrinkage and mechanical stability can be achieved while at the same time giving rise to a smooth flooring contact surface which is of benefit in some installation practices where carpet tile must be maneuvered into position by sliding across a flooring surface or where a peel-away adhesive sheet or pre-applied pressure sensitive adhesive is to be used.
As will be appreciated by those of skill in the art, the production and subsequent patterning of carpet tiles may necessitate the exposure of the carpet structure to elevated temperatures for significant periods of time. By way of example, a carpet composite may undergo post-cure heating at temperatures between 250.degree. F. and 325.degree. F. for between about 2 minutes and 8 minutes. The subjection of the carpet to these types of temperatures requires that the backing material be resistant to unreasonable heat shrinkage which can lead to cupping of a carpet tile as well as being resistant to stretching which can lead to curling of a carpet tile.
At the same time, it is desirable to be able to fuse the fibers on the floor contacting surface of the backing material with heat to provide a smooth contacting surface. While some cupping yielding a slightly domed configuration to the tile may be acceptable and, in fact, desirable in some instances, curling is unacceptable in that it gives rise to numerous process disadvantages including difficulty in patterning in later stages. Prior to the present invention it was believed that a nonwoven backing containing 80 percent polyester and 20 percent polypropylene would provide the preferred resistance to curling. It has been determined that this curl resistance can be improved by increasing the percentage of polypropylene significantly thereby giving rise to slightly greater heat shrinkage but surprisingly without the occurrence of unreasonable levels of cupping.